Aqueous polymer compositions

ABSTRACT

Aqueous polymer compositions which contain a polymer having ureido groups and a polyaldehyde compound are suitable for the production of coatings having high adhesion to substrate and having high cohesion.

EXAMPLE

a) Preparation of Aqueous Polymer Dispersions D1 to D3 and DV (Comparison)

D1: In a polymerization vessel, 200 g of water, 75 g of feed 1, 25 g of feed 2, 12.5 g of a 20% strength by weight aqueous solution of a mixture of ethoxylated fatty alcohols (C_(16/18), degree of ethoxylation: 18, emulsifier 1) and 2.5 g of a 20% strength by weight aqueous solution of the active substance corresponding to Dowfax 2A1 (emulsifier 2) were mixed with one another and the mixture was heated to 85° C. Thereafter, the mixture was kept at 85° C. for 15 minutes and, while maintaining the polymerization temperature, the remaining amount of feed 1 was then added to the polymerization vessel (in the course of 2 hours) and, beginning at the same time, the remaining amount of feed 2 was introduced (in the course of 2 hours 15 minutes). The system was then left to stand for a further 2 hours at 85° C. while stirring. After the mixture had cooled to room temperature, 12 g of a 10% strength by weight aqueous sodium hydroxide solution were added.

The LT value of the resulting dispersion was 78 and the solids content was 48.9% by weight.

Feed 1:

187 g of water,

25 g of 20% strength by weight aqueous solution of emusifier 1,

37.5 g of 20% strength by weight aqueous solution of emulsifier 2,

15 g of 50% strength by weight aqueous solution of acrylamide,

13.5 g of methacrylic acid,

10 g of N-(2-methacryloyloxyethyl)-ethyleneurea as active monomer II,

150 g of methyl methacrylate and

350 g of n-butyl acrylate

Feed 2:

100 g of water and

2.5 g of sodium peroxodisulfate

DV: As for D1 but without the active monomer II in feed 1.

Solids content: 49.6% by weight, LT value: 76.

D2: As for D1 but feed 1 comprised 18 g instead of 10 g of the active monomer II.

Solids content: 50.3% by weight, LT value: 76.

D3: As for D1 but feed 1 contained 150 g of styrene instead of 150 g of methyl methacrylate.

Solids content: 49.6% by weight, LT value: 63.

b) The following aqueous polymer systems S and SV (comparison) were prepared from 100 ml of each of the aqueous polymer dispersions from a) by stirring in Zg of a 40% strength by weight aqueous solution of glyoxal:

    ______________________________________     Polymer     Dispersion     system      used        Z [g]  Ratio R     ______________________________________     SV1         DV          0      --     SV2         DV          0.32   0     SV3         D1          0      --     S1          D1          0.08     1:0.25     S2          D1          0.16     1:0.5     S3          D1          0.32   1:1     S4          D1          0.65   0.5:1     SV4         D3          0      --     S5          D3          0.32   1:1     SV5         D2          0      --     S6          D2          0.28     1:0.5     S7          D2          0.56   1:1     ______________________________________

c) Testing of Films of the Polymer Systems S and SV for Cohesion

About 500 μm thick polymer films were prepared from the polymer systems from b) by forming a film in a silicone pan from a defined amount of polymer dispersion over a period of 4 days at 23° C. and 50% relative humidity, and the films were subjected to the following tests:

1. Determination of the swelling value Q

2 cm² square film pieces were placed in 100 ml of tetrahydrofuran (THF) for 24 hours at room temperature. The swelling value Q is the THF absorption by the sample, based on the mass of the initial sample in % (determined gravimetrically). The larger Q, the lower is the cohesion.

2. Determination of tensile strength K [N/mm² ] and elongation at break D [%]

These tests were carried out according to DIN 53504, at a take-off speed of 200 mm/min, a test temperature of 23° C. and with the use of sample shape S2. The larger K and the smaller D, the more pronounced is the cohesion.

The results obtained are shown in Table 1 below:

                  TABLE 1     ______________________________________     Polymer     system    Q              K     D     ______________________________________     SV1       963            2.7   546     SV2       943            2.7   545     SV3       712            3.5   504     S1        593            4.0   416     S2        541            4.2   369     S3        487            4.5   338     S4        476            4.0   304     SV5       650            4.7   468     S6        428            6.4   297     S7        365            6.9   240     ______________________________________

d) Preparation of a Coating Material

Coating materials were formulated from the polymer systems S and SV according to the following recipe:

    ______________________________________     Water                      89     g     25% strength by weight aqueous solution of the sodium                                6      g     salt of a copolymer of maleic acid and diisobutylene     (dispersant for pigments and fillers)     Parmetol ® A23 (preservative)                                2      g     Natrosol ® 250 HR (4% strength by weight aqeuous                                9      g     thickener solution based on hydroxyethylcellulose)     Propylene glycol           32     g     Butyldiglycol              10     g     Agitan ® 702 (antifoam)                                4      g     Kronos ® RHD-2 (finely divided TiO.sub.2 pigment)                                210    g     Talc SE Micro (filler)     106    g     Collacral PU 75 (polyurethane associative thickener)                                10     g     Butyldiglycol              13     g     Kristallol ® K60 (hydrocarbon mixture as film                                5      g     formation assistant)     Polymer system S or SV     504    g     ______________________________________

e) Testing the Wet Adhesion of the Coating Materials from d) on an Alkyd Resin Coat

First, a high-gloss solvent-containing alkyd resin coating material was applied to a PVC film to give a layer which was 120 μm thick when wet, and the layer was dried for one day at room temperature and for 7 days at 50° C. in a through-circulation drying oven. Thereafter, a 200 μm thick wet layer of a coating material from d) was applied to the alkyd resin coat and was dried for 3 days at 23° C./65% relative humidity. Thereafter, the coat surface was damaged by cutting with a knife, and the films prepared in this manner were subjected to a plurality of successive frost-thaw cycles to test the wet adhesion of the topcoat on the alkyd resin basecoat. Within one frost-thaw cycle, the coated films were first stored for 8 hours in water, then kept for 16 hours at -20° C. and then placed in water for 10 minutes at 23° C. After each frost-thaw cycle, the adhesion of the topcoat on the basecoat was tested at the incision. The wet adhesion results are shown in Table 2.

                  TABLE 2     ______________________________________     Basic polymer system     SV1      SV3       S3        SV4     S5     ______________________________________     1st   poor   completely                            completely                                    completely                                            completely     F-T          satisfactory                            satisfactory                                    satisfactory                                            satisfactory     cycle     2nd          completely                            completely                                    completely                                            satisfactory     F-T          satisfactory                            satisfactory                                    satisfactory     cycle     3rd          completely                            completely                                    completely                                            satisfactory     F-T          satisfactory                            satisfactory                                    satisfactory     cycle     4th          completely                            completely                                    completely                                            satisfactory     F-T          satisfactory                            satisfactory                                    satisfactory     cycle     5th          completely                            completely                                    completely                                            satisfactory     F-T          satisfactory                            satisfactory                                    satisfactory     cycle     6th          completely                            satisfactory                                    satisfactory                                            satisfactory     F-T          satisfactory     cycle     ______________________________________ 

We claim:
 1. An aqueous polymer composition containingA) at least one polymer A dissolved or dispersed in an aqueous medium and composed of polymerized monomers having at least one ethylenically unsaturated carbon-carbon bond, with the proviso that the polymer A has at least one group of the formula I ##STR1## where X is O or S andR¹ and R² each hydrogen or C₁ -C₅ -alkyl or both together form a bridging C₂ -C₄ -alkylene group which may be monosubstituted or disubstituted by C₁ -C₄ -alkoxy and/or by hydroxyl, B) at least one chemical compound B having at least two unprotected and/or reversibly protected aldehyde groups, with the proviso that the molar ratio R of the total amount of groups I contained in the aqueous polymer composition to the total molar amount of unprotected and/or reversibly protected aldehyde groups contained in said composition in the form of compounds B is from 0.1:1 to 10:1,and C) no hydrazide.
 2. An aqueous polymer composition as claimed in claim 1, whose polymer A contains, as group I, a group of the formula ##STR2## where each of the two substituents R³ and R⁴ may be hydrogen, hydroxyl or C₁ -C₄ -alkoxy.
 3. An aqueous polymer composition as claimed in claim 1, whose polymer A contains monomers having groups I, in polymerized form, in amounts of from 0.1 to 30% by weight, based on the total amount of the monomers polymerized in A.
 4. An aqueous polymer composition as claimed in claim 1, containing glyoxal as chemical compound B.
 5. An aqueous polymer composition as claimed in claim 1, containing a polymer A as chemical compound B.
 6. A process for the preparation of an aqueous polymer composition as claimed in claim 1, wherein a monomer mixture which comprises monomers which have a group I is polymerized by the free radical aqueous emulsion polymerization method, and a chemical compound B is stirred into the resulting aqueous polymer dispersion.
 7. An aqueous polymer composition as claimed in claim 1, containingfrom 5 to 50% by weight of polymer A, from 5 to 75% by weight of inorganic fillers or pigments, from 0 to 15% by weight of conventional coating assistants, at least one chemical compound B in an amount such that R is from 0.1:1 to 10:1 and water. 